The invention relates to an antenna device comprising a radiation electrode that extends two-dimensionally. The invention further relates to a printed circuit board and to a mobile radio apparatus
As mobile communication equipments such as mobile radio apparatus, e.g. telephones have been commonly used, their size needs to be made smaller. In recent years, in order to meet this requirement, chip type antennas, for example, have been developed for the mobile communication equipments.
Since a chip antenna can be rather small in comparison with a monopole type antenna, the mobile communication equipment itself can be also made smaller by use of the chip antenna. On the other hand, however, there exists a problem that the bandwidth of the chip antenna may become narrow due to the small size of the antenna.
Accordingly, it is an object of the invention to provide an antenna device that is small in its size but wide in its bandwidth.
In order to achieve the above-described object, the invention provides an antenna device comprising a substrate and a radiation electrode which extends two-dimensionally and is formed on a surface of or inside the substrate wherein the substrate has a hollow part or a recess.
The hollow part or recess formed in the substrate provides an effect of widening the bandwidth of the antenna device.
Especially, the substrate for the antenna device in accordance with the invention preferably contains a dielectric material or a magnetic material. Either dielectric material or magnetic material may be used as a material for the substrate depending on the applications. In particular, the dielectric material can provide an antenna that has a favorable high frequency characteristic.
Besides, the antenna device in accordance with the invention is preferably constructed in such manner that a recess extending from a front surface to a rear surface of the substrate is formed in a lower surface of the substrate, first and second grounding electrodes are formed respectively on both sides of that portion of the lower surface of the substrate where the recess is formed, and an shorting electrode is formed on one of the front surface and the rear surface of the substrate for connecting the radiation electrode to each of the first and second grounding electrodes.
With the shorting electrode as formed above, the bandwidth of the antenna device can be further widened.